Known in the art are methods for recovering metals belonging to Groups V-VI of the periodic system which can be classified into three groups.
The first group includes methods based on the use of versatile ionites. Thus, U.S. Pat. No. 4,046,688 teaches the use of strongly-acidic cationites in the H-form for the removal of antimony from an aqueous solution, provided that antimony is present in the cation form, and from strongly-basic resins in the OH-form, provided that antimony is present in the anion form. This method, however, is not suitable for industrial liquors, wherein components capable of anionic and cationic exchange are present, as a rule, in considerable amounts.
The second group includes methods also based on the use of versatile ionites, with the only difference that the starting liquors are preliminary treated to convert the metal being recovered to the condition preferably for ion-exchange bonding. Thus, in U.S. Pat. No. 3,689,217 to ensure an enhanced sorption of arsenic on a strongly-basic anionite, the starting liquor is charged with chlorine-containing reagents such as hydrochloric acid or ammonium chloride in a molar excess of 10-200 relative to the amount of arsenic. Disadvantages of this method includes the necessity of performing the above-mentioned preliminary treatment which complicates the process.
The last group involves methods based on the use of special-purpose ionites selectively reacting with metals belonging to Groups V-VI of the periodic system. These methods have advantages residing in a high degree of recovery of said metals owing to the selective effect of the ionites employed. Thus, U.S. Pat. No. 3,887,460 teaches recovery of arsenic by means of ionites produced by conversion of preliminarily complexed reagents such as boron-containing complexes of salicylic or gallic acid to a polymeric structurized condition.
Despite the above-mentioned selectively, the above-mentioned ionites do not provide for a required depth of recovery of arsenic; the maximum possible degree of recovery of arsenic does not exceed 82%. The process of combining arsenic occurs quite slowly and it takes about 3 days to achieve the equilibrium. These disadvantages are possibly the result of the fact that in the preparation of ionites with the use of precomplexed monomers it is substantially impossible to efficiently and intentionally carry out structurization reactions with polymers to form the required reticulated three dimensional structures. Moreover, the above-described technique is unsuitable in the cases where monomers after coordination lose their reactivity in the processes of polymer formation.
In 1950 A. S. Smirnov and M. M. Bluvshtein proposed to use products of polycondensation of polyhydric phenols with formaldehyde for selective recovering of heavy metals (cf. "Doklady Akademii Nauk SSSR, 1950, No. 3, pp. 449-451).
The thus-proposed, sorbents, unfortunately, had an imperfect structure due to the formation thereof at elevated temperature and evaporation of water.
As a result, complexon radicals fixed in the three-dimensional reticulation of ionites become hardly accessible for the reaction of coordination bonding.
For this reason, ionites based on polyhydric phenols have not found a wide application hitherto and the attempts to practically realize the expected specificity and selectivity thereof have been unsuccessful.
Therefore, selective ionites of the prior art do not provide the required separation, i.e. a high degree and speed of recovery of metals.